Another Rainbow Islands on the bench, this one from my friend “Mikidaffy1983”:

Board was in excellent state but when powered on all I got was a screen of wavy lines:

Started my usual visual inspection and didn’t notice nothing odd but when touched the PAL “B22-05” @IC33 I found it quite hot.Probing its outputs I found they were almost all dead so I programmed a GAL16V8 with the replacement hosted on this site (thank you Porchy and Macro for this).With the PAL replacement fitted the board succesfully booted but sometimes stuck on a static black/white striped screen , others times with bad/missing backgrounds:

Since I repaired other Rainbow Islands (and similar hardware like Bonze Adventure) I knew tiles are generated by the custom marked ‘PC080SN’ @IC34.This custom is connected to two 62256 SRAMs so I analized them with a logic probe and found that most DATA lines of the one @IC3 were stuck HIGH or LOW.Without thinking twice I desoldered and tested it having confirm it was bad:

Fitted a new 62256 SRAM led me to this point:

All backgounds/tiles were restored but there was a clear issue with the blue color.As we know RGB colors are generated by the custom module ‘TC0070RGB’ which on this PCB was resoldered but after a comparison with a good board I couldn’t find anything strange so I decided to move ahead and look into other issues.In particular there was no sound at all, only a buzzing noise sign that the main MB3735 amplifier was good.There was also no sound ouput from YM3012 DAC and this convinced me look into the digital part of the audio circuit.Probing the 6264 SRAM  @IC44 revealed weird activity on its DATA/ADDRESS lines, testing it out-of-circuit confirmed it was bad:

Sound was fully restored but it was quiete and faint also at the highest volume.Connecting an external AMP to the inputs of the TL074 OP-AMP @IC67 gave me strong and steady volume so I rightly replaced this IC.

Back to the blue color issue I decided to go straight and remove the TC0070RGB module installing the Macro replacement resulting in a success.Board 100% fixed.

Another TAITO PCB on the bench.This time we have a Rainbow Islands one:

The first thing I noticed was (dust apart..) the lack of the TC0070RGB module.For the uninitiated this custom in SIL package is a DAC so it converts digital RGB output of the PCB into analog signals.I borrowed this custom from my Bonze Adventure PCB and installed the needed sockets as always.Once powered on the board, I was greeted by a solid black screen so I started investigating.Probing the main 68000 CPU I found there was no clock at all.Main clock is generated by a 16MHz oscillator @X1 and then divided by a near 74LS161 counter.I visually inspected this part of circuit and found this:

Replaced the oscillator gave me a fully working board but then it was time to find a proper replacement for the borrowed TC0070RGB.I knew this custom was reverse-engineered by Macro (thanks to him) some time ago:

https://www.arcades.plus.com/Taito-RGB.html

https://www.arcades.plus.com/Taito-RGB-Instructions.html

So I order a couple of bare PCBs and assembled one:

I can say it works like the original part, no differences at all, I higly recommnend this replacement.

First of all I want to thank JROK for providing me all the technical info and allowing its public release, without his help I would not have ever made.Let’s start with the story.

Some time ago a  friend of mine sent me his Splatterhouse PCB bought as working saying it got stuck upon boot  on ‘ROM TEST START!! PLEASE WAIT..’ message displayed upside down on a screen filled with red zero.So I started to investigate on the net and found that usually this kind of issues are caused by a faulty custom chip marked ’64A1′ @M4 on ROM board.This was confirmed by swapping this IC in another CPU board of Galaga88 with this missing component , in this case I got an ‘EEPROM ERROR’ message which is a further proof of the fault.

Thanks always to JROK we know that this ’64A1′ custom IC is nothing else than a HD63701 MCU with the exception of two custom opcodes not present in original part.You can go deeper into technical reading here:

https://www.jrok.com/hardware/cus60/cus60_an_owners_guide.html

So, programming a blank HD63701 MCU with the available dump from MAME won’t work due the presence of these two custom opcodes.So, patching a ROM is needed.

In the specific you have to change three bytes in the ROM  “VOICE0” at a specific offset.For example :  in Splatterhouse the offset is $FA8B and the new HEX values are “20 01 56”.

The string to search for in HEX is  “B7 C0 00 6E 00” and the first 3 bytes must be changed to  “20 01 56”

The patch seems to be needed at offset $FA8B for most games, but not all. Here’s a reference table :

Tank Force – $FA29
Blazer – $FA8B
Dragon Spirit – $FA8B
Galaga 88 – $FA8B
Marchen Maze – $FA8B
Splatterhouse -$ FA8B
Rompers – $FA8B
Blast Off – $FA8B
World Court – $FA8B
World Stadium (and WS ’89, WS ’90) – $FA8B
Bakutotsu Kijuutei (Baraduke 2) – $FA8B
Beraboh Man – $FA4E
Dangerous Seed – $FA8B
Face Off – $FA29
Pisto Daimyo no Bouken – $FA8B
Puzzle Club – no voice ROM !
Quester – $FA1B
Souko Ban Deluxe / Boxy Boy – $FA8B
Yokai Douchuuki (Shadowland) – $FA8B

So, it was only matter to find some real blank HD63701.My first attempt failed since I bought as new some ICs that they turned out to be already programmed and, since they were the plastic HD637B01VOP one-time-progfammable version, they were unusable for my purpose.But then I was luck and found some HD63701VOC UV erasable ones:

So, it was only matter to program one of these MCU with MAME dump using my Hi-Lo Systems ALL-11C EPROM programmer and, at the same time, replace the ROM ‘VOICE0’ with the properly patched one.Once done, I had confirmation of what the good JROK said about. Operation  ‘NAMCO custom 64A1 replacement’ accomplished.